Deprotonation of the Transition Metal Hydride (η⁵-C₅Me₅)(PMe₃)IrH₂. Synthesis and Chemistry of the Strongly Basic Lithium Iridate (η⁵-C₅Me₅)(PMe₃)Ir(H)(Li)

Treatment of (η5-C5Me5)(PMe3)IrH2 (1) with tert-butyllithium gives (η5-C5Me5)(PMe3)Ir(H)(Li) (2) as a bright yellow solid. NMR evidence indicates that the lithium iridate 2 is aggregated in benzene, is converted to a single symmetrical species in THF, and is present as a dimer in DME. Treatment of 2 with 3,3-dimethylbutane trifluoromethanesulfonate-1,2-syn-d2 (3-syn-d2) gave the alkylated hydridoiridium complex 4a-anti-d2, which was converted to the corresponding chloride Cp*(PMe3)Ir(CHDCHDCMe3)(Cl) (4c-anti-d2) by treatment with CCl4. Analysis of this material by NMR spectroscopy showed that it was contaminated with ≤15% syn isomer. The alkylation therefore proceeds with predominant inversion of configuration at carbon, indicating that the major pathway is an SN2 displacement and not an outer-sphere electron-transfer reaction. Protonation studies carried out on iridate 2 with organic acids of varying pKa allowed us to estimate that the pKa of the dihydride 1 falls in the range 38−41, making it less acidi...